A phenylethynyl Fischer carbene complex was used as a traceless directing group for the regioselective cycloaddition of dithiolethiones to arylacetylene, which constitutes the first synthesis of E-dithiafulvene thione or dithioesters.
We report the synthesis of some new polysulfur-nitrogen heterocycles by cycloaddition reactions to readily available tricyclic condensed 1,2-dithiole-3-thiones. Thus, treatment of bis[1,2]dithiolopyrrole ketothione 1 with diacyl acetylenes gave the bis-aducts 2a-d. On the other hand, cycloaddition of bis[1,2]dithiolo[1,4]thiazine ketothione 3 with 1 equiv of acyl or diacyl acetylenes gave [1,3]dithiolylidenyl[1,2]dithiolo[1,4]thiazines 4a-f in fair to high yields. Catalysis by scandium triflate was used in the reactions that implied the less reactive dipolarophiles. Treatment of 3 with 2 equiv of DBA gave the bis-aduct 5a, and reaction of 4c with DMAD gave the mixed bis-adduct 5b. Cyclic voltammetry of selected examples showed irreversible processes that were influenced by the electrochemical activity of peripheral groups bonded to the heterocyclic system.
[reaction: see text] Tricyclic 4-ethyl-5-thioxo-3H,5H-bis[1,2]dithiolo[3,4-d][4,3-b]pyrrol-3-one and monocyclic 3H-1,2-dithiole-3-thione derivatives reacted with Fischer carbene complexes, giving 1,3-dithiin dithioortho esters through insertion of the carbenic carbon into the S-S bond next to the thiocarbonyl function of the substrate.
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